1. Field of the Invention
The present invention relates to a pickup device including a flexible circuit member in which an anti-noise measure is implemented and cost reduction is achieved.
2. Description of the Related Art
FIG. 14 is a diagram showing a conventional pickup device 501.
“LD” is an abbreviation of “laser diode”, while “LDD” is an abbreviation of “LD driver”. LDD 510 is a laser driver circuit for driving an LD 520 to emit laser light. Electric current is made to flow from the LDD 510 to the LD 520, and laser light is output from the LD 520. “LDD” may be referred to as a “laser driver”. By means of laser light emitted from the LD 520 by supplying an electric current from the LDD 510 to the LD 520, information can be recorded on a disc 700, and information recorded on the disc 700 can be reproduced.
The laser light output from the LD 520 is irradiated on the disc 700 via a diffraction grating 530, intermediate lens 540, half mirror 550, and objective lens 560. A portion of laser light reflected off of the disc 700 is input into PDIC 570 or the like. “PDIC” is an abbreviation of “photo diode IC”. Upon receipt of the light, the PDIC 570 converts the light signal into an electric signal, and outputs the electric signal for use in operating a servo mechanism (not shown) of a lens holder (not shown) of the pickup device 501.
Further, a portion of the laser light output from the LD 520 is introduced into the FMD 580. “FMD” is an abbreviation of “front monitor diode”. The FMD 580 monitors the laser light output from the laser diode so as to provide feedback control of the laser diode.
The LDD 510, LD 520, diffraction grating 530, intermediate lens 540, half mirror 550, objective lens 560, PDIC 570, and FMD 580 are mounted on a housing (not shown). The LDD 510, LD 520, PDIC 570, and FMD 580 are electrically connected to an FPC 505. “FPC” is an abbreviation of “flexible printed circuit”. The FPC 505 may be formed by printing in parallel a plurality of circuit conductors composed of a metal foil such as copper foil on an insulating sheet, and further providing a protective layer on top. The optical pickup device 501 is configured with the above-described various components. The optical pickup device 501 may further comprise other components which are not shown in FIG. 14 for simplification of the drawing.
The optical pickup device 501 is used to reproduce and record data (such as information) on a medium. Examples of the media include various optical discs such as read-only optical discs including CD-ROM and DVD-ROM, write-once optical discs including CD-R, DVD-R, and DVD+R, and writable/erasable or rewritable optical discs including CD-RW, DVD-RW, DVD+RW, and DVD-RAM.
“CD” is an abbreviation of “compact disc”. “DVD” is an abbreviation of “digital versatile disc” or “digital video disc”. “ROM” in “CD-ROM” and “DVD-ROM” is an abbreviation of “read only memory”. As such, CD-ROM and DVD-ROM are for reading only. “R” in “CD-R”, “DVD-R”, and “DVD+R” is an abbreviation of “recordable”. As such, CD-R, DVD-R, and DVD+R are recordable. “RW” in “CD-RW”, “DVD-RW”, and “DVD+RW” is an abbreviation of “rewritable”. As such, CD-RW, DVD-RW, and DVD+RW are rewritable. “DVD-RAM” is an abbreviation of “digital versatile disc random access memory”, and denotes an optical disc that is readable, writable, and erasable.
The optical pickup device 501 allows reproduction of data recorded on various optical discs and recording of data on various recordable and rewritable optical discs. In order to improve the S/N ratio in relation to noise generated from various components mounted in the optical pickup device 501, an FPC having two conductive layers may be employed. S/N denotes the ratio of signal to noise. The signal and noise are indicated in units of dB (decibels). Noise refers to disturbances in electric signals and undesired sounds.
As an example FPC having two conductive layers, FIG. 15 depicts a double-sided flexible printed circuit board in which warping of the board is prevented so as to facilitate handling of the board and to increase yield of the boards assembled with components.
FIG. 15 is a diagram for explaining one example of a conventional double-sided flexible printed circuit board.
The double-sided flexible printed circuit board (FPC) 801 is curved along a curve center line L. A curvature 820 is formed in a wiring portion 810 provided on one side. A conductive pattern 802 is formed on the front S-side surface (denoted in FIG. 15) of the base film 806 constituting the FPC 801. Further on top, a photosensitive cover layer 804 is overlapped so as to insulate the conductive pattern 802. The photosensitive cover layer 804 may be referred to as a “photo-imageable cover layer” and abbreviated as PIC. On the rear T-side surface (denoted in FIG. 15) of the base film 806 constituting the FPC 801, a pseudo conductive pattern 803 for reinforcement is provided in regions other than the portion near the curve center line L. A photosensitive cover layer 805 for insulating the pseudo conductive pattern 803 is provided covering the pseudo conductive pattern 803.
On the rear T-side surface of the wiring portion 810 provided on one side of the FPC 801, the reinforcing conductive pattern 803 and the PIC layer 805 are absent at a portion near the curve center line L, namely, between M-M. The conductive pattern 802 and the PIC layer 804 are provided around the curve center line L on the front S-side surface alone.
In recent years, there have been increasing requests for higher speeds in performing a recording operation with respect to the optical disc 700 (FIG. 14) such as a CD-R. However, if the recording operation speed with respect to the optical disc 700 such as a CD-R is increased in the pickup device 501 including the FPC 505 having a conventional design, there is a risk that noise would be generated due to various signals such as analog and digital signals which are input into and output from components such as the LDD 510, PDIC 570, and FMD 580. The noise may be generated in an area surrounding the portion at which the LDD 510 is mounted on the single-sided FPC 505, and from the LD 520 for a CD. The term “analog” denotes that a state of a substance or a system is represented by continuously variable physical quantities. “Digital” denotes that a state of a substance or a system is represented by signals composed of discrete numbers or letters.
When noise is generated, because of crosstalk among signals in the LD 520 for a CD, in areas surrounding the LDD 510, in the PDIC 570, and in the FMD 580, influence of the noise may reach into a low-power analog signal which is transmitted through the single-sided FPC 505. As a result, the pickup device 501 fails to perform normal operations. “Crosstalk” denotes a level of interference generated at a transmitting end of a signal line.
In order to prevent noise caused by an analog or digital signal from influencing the low-power analog signal transmitted through the single-sided FPC 505, an FPC 801 comprising two conductive layers 802, 803 (FIG. 15) may be employed. The FPC 801 comprising two conductive layers includes a conductor member 802 on one side and a conductor member 803 on the other side, and is configured as one integral unit having the two layers on the respective sides.
The FPC 801 comprising the two conductive layers 802, 803 and having an anti-noise measure implemented therein is next described in detail. By reinforcing GND 803 of the FPC 801, which corresponds to one of the conductive layers of the FPC 801 comprising two conductive layers, undesired influence of a digital or analog signal on the low-power analog signal can be avoided. For example, by employing the FPC 801 comprising the two conductive layers 802, 803 shown in FIG. 15 in the pickup device 501 (FIG. 14) in place of the single-sided FPC 505 shown in FIG. 14, the S/N ratio of the pickup 501 can be improved. “GND” is an abbreviation of “ground” and denotes electrical grounding.
When the flexible circuit member 801 is configured in the form of the FPC including the two conductive layers 802, 803, the flexible circuit member 801 becomes expensive. The cost of the flexible circuit member 801 configured in the form of the FPC including the two conductive layers 802, 803 (FIG. 15) is approximately double the cost of the flexible circuit member 505 (FIG. 14) configured in the form of a single-sided FPC. By providing the flexible circuit member 801 including the two conductive layers 802, 803 integrated into one component in a pickup device 501 (FIG. 14), the product unit price of the pickup device 501 becomes increased. Accordingly, there exists a need for a pickup device which includes a flexible circuit member with an enhanced S/N ratio and for which cost increases are minimized.